Heretofore, in winding or rewinding a web, a dancer roll has been used for the purpose of absorbing tension variation and thereby controlling tension in the web. However, dancer rolls can create creases in thinner films so that the edges of the wound films cannot be aligned. Furthermore, dancer rolls imparts tension into the web of material being wound. In some winders, a method of adjusting tension by controlling the torque of a motor shaft is generally employed or the tension is detected by means of a fixed roll.
A typical means for detecting tension exerted upon a sheet and controlling the same is by the use of a dancer roll. The tension exerted upon the sheet is detected as an electric signal derived from a displaced dancer roll actuating a potentiometer or the like. After comparing this detected signal with a preset value, a driving force is controlled so as to bring the dancer roll back to its set position, thereby exerting tension upon the sheet to a predetermined value. This type of apparatus has a disadvantage in that the follow-up characteristic of a dancer roll, i.e., its response to film tension, is not sufficiently high. In addition, by definition, there is always some amount of tension that the dancer must impart into the web to properly monitor and operate the drive control. Thus, a typical dancer arrangement cannot be used to achieve zero tension in the web being wound.
Another method employed to control tension is an apparatus in which current through a motor for driving a spool or core is detected (when the tension of a sheet being taken up becomes small, the torque of the motor is reduced and thus the current through the motor is reduced) and thereby the tension exerted upon the sheet is detected. In order to compare the tension of the sheet with a preset value, the detected current signal is led to a current control system in which the current signal is compared with a preset current value for the motor in order to control the motor current. However, this type of apparatus also involves problems in that the response characteristic for tension control is poor because of the inertia of the mechanical system, and the sheet is unevenly stretched owing to variations in tension.
Assuming that controls similar to those in the aforementioned winders are employed in a rewinder, since such material as sound film is generally kept intact for several days for aging purposes before it is rewound by a rewinder, air wound jointly with the film escapes resulting in an eccentric deformation of the wound film. As a result, variation in tension is far larger than that which occurs upon winding, and the rewinding becomes impossible.
As described above, there are many disadvantages in the prior art methods. More particularly, in a rewinder having a dancer roll, tension of a film cannot be measured precisely because of the mass of the dancer roll, and the r.p.m. of the spool becomes equal to or higher than the resonant frequency of the vibration system consisting of the mass of the dancer roll, the bracket supporting same and the spring or other type of tensioning mechanism used for the dancer roll. Thus, not only does the capability of detecting tension diminish, but also the rewinding operation per se becomes impossible because of the vibration of the dancer roll. As stated previously, a wound film is kept intact for several days for the purpose of aging.
Furthermore, assuming that controls similar to those in the aforementioned winders are employed in a rewinder, since such material as polyethylene foam or the like, go through an aging process in which the web of material experiences post expansion, and since the web of material wound into a roll is confined to a given space, any expansion of the web of material that does take place is mirrored by an equal amount of compression of the web of material in other parts of the roll. In general, the outer layers of the web in the roll will expand and as they expand, they compress the inner layers of the web within the roll. As a result, variation in thickness in the web of material tends to remain in the web of material even after its is rewound using conventional winding methods.
In addition, most thermoplastic film or sheet experiences some stretching during processing. If controls similar to those in the aforementioned winders are employed in a winder or a rewinder, the amount of stretching that occurs tends to remain in the of material until it is unwound and left in a free state without any external forces. Over time the of material will tend to contract and relax in the direction of the stretch and assume a new dimensional geometry. If a product is die cut, for instance, before the product has reached a relaxed state, then dimensions of the cut product will change once the product relaxes and its dimensions may exceed the acceptable tolerances and it may have to be discarded as scrap.
Other post processing operations such as skiving or thermoforming often requires a material that has low stress in it. However, using controls similar to those in the aforementioned winders or rewinders, some stress and orientation can be imparted into the material.
Winders are an important apparatus in many manufacturing processes, such as in the manufacture of cable, film, sheet or other strand or web type materials which have many beneficial industrial and commercial uses particularly in the packaging industry. The method and apparatus employed by winders are described in the U.S. patents listed below as well as in other literature pertaining to the design and method of operation.
U.S. Pat. No. 3,429,517 discloses a double layer winding device, especially for textiles webs, which operates in conformity with the duplex winding with two hank rollers of changing direction of rotation for storing the goods which are withdrawn in a continuous uninterrupted process.
U.S. Pat. No. 3,503,526 describes an apparatus for winding or unwinding continuous webs of non-conductive material, the apparatus incorporating an alpha particle-emitting device directed toward a winding or unwinding roll or web beyond the point of tangency between the web and roll.
U.S. Pat. No. 3,506,211 discloses an apparatus for cutting and coiling webs of paper, corrugated cardboard, and the like, comprising a coiling bar in the form of a shaft which is activated at one end and mounted at the other end in a removable bearing which makes use of a mechanical movable arrangement along the winding bar.
U.S. Pat. No. 3,514,046 describes an apparatus including a pair of windup reels selectively positionable to be driven for winding up a strip of material received from an adjacent processing apparatus.
U.S. Pat. No. 3,514,047 describes an apparatus including a utilized surface windup device for automatically introducing a core within the nest of the winding drums, cinching the end of a web around the core, winding the web onto the core to form a roll, and ejecting the wound roll from the nest. The reference also discloses a method for automatically attaching the trailing end of the web to the outer convolution of a wound roll and a method for automatically cleaning the winding drum.
U.S. Pat. No. 3,602,448 describes an apparatus for winding a web onto a rotating reel, an ironer assembly for smoothing the web as it is added to the reel, including an ironer roll which rides on the reel, a pivotally suspended frame larger in mass than the ironer roll, and springs under compression between the frame and roll for resiliently supporting the frame on the roll, so that the weight of the frame augments the pressure exerted by the roll on the web.
U.S. Pat. No. 3,630,462 describes a web winding an apparatus including a reel on which a roll being wound is contacted by a rider roll. A potentiometer associated with the rider roll monitors the roll buildup and controls a DC-indexing motor to rotate the winding-roll away from the rider roll to maintain substantially constant web tension. A circuit controls the acceleration and deceleration of the indexing motor as the rolls are being changed to permit web tension to be maintained constant.
U.S. Pat. No. 3,677,484 describes a thin layer material having a large width which can be wound up around a winding core by continuously supplying and inserting an elongated continuous yarn-like material, and which transverses the thin layer material, in between one wound layer and another, to leave a clearance along the inserted yarn-like material.
U.S. Pat. No. 3,749,328 describes an air-permeable member which is secured to the end of a tube carried by a pivotally-mounted guide arm, said member being positioned between the flanges of a tape reel and mechanically biased toward the reel hub as a strip of tape is wound onto the hub.
U.S. Pat. No. 3,794,268 describes a method and apparatus for winding a hollow, flexible tubular material in a manner which permits the tubular material to be removed from its support and simultaneously filled continuously for packaging or other purposes.
U.S. Pat. No. 4,050,642 describes a method and apparatus for winding a film wherein a pressurized jet of air is directed onto a surface of an unsupported portion of the film being wound or rewound.
The above mentioned patents do not disclose the method and apparatus for reducing the tension of the sheet or web as it is wound, or reducing roll compression exerted by a lay-on roll when surface winding through the use of a secondary lay-on roll with a differential speed adjustment relative to the primary lay-on roll speed, or the use of a torque motor to control the pressure exerted between the roll being wound and the lay-on roll that turns the roll being wound. When less tension or compression was desired in a material wound on a roll, it has previously been necessary to loosen the material on the wound roll after winding or rewind the roll in a secondary operation off-line. This additional procedure adds labor, and therefor costs, to the product, and moreover, results in added handling and exposure of the material to the potential of marking, soiling, crimping, and/or types of damage that result in poor aesthetic and/or functional qualities, reducing the value of the material and/or its structure. Furthermore, these patents do not disclose the use of a roll surface made up of a material that is softer than the web of material being wound and thus the roll with a soft covering behaves more like a flat surface which reduces point to point contact that most surface winders exhibit. In addition, a tucking device or tucking roll is not disclosed in the above patents nor is a retractable cutting roll and knife assembly to cut the web of material.